共面双对称几何条件下Ne原子(e,2e)反应的三重微分截面

利用标准一阶扭曲波玻恩近似方法（DWBA）计算了共面双对称几何条件下不同能量电子碰撞电离Ne原子的三重微分截面(TDCS),与Nixon和Murray 最新的实验测量数据进行比较.当入射电子能量较低时,理论计算结果和实验数据符合较差;随着入射电子能量的增加,而符合程度逐渐改善.     

共面双对称几何条件下Ne原子(e,2e)反应的三重微分截面

利用标准一阶扭曲波玻恩近似方法(DWBA)计算了共面双对称几何条件下不同能量电子碰撞电离Ne原子的三重微分截面(TDCS),与Nixon和Murray[1]最新的实验测量数据进行比较.当入射电子能量较低时,理论计算结果和实验数据符合较差;而随着入射电子能量的增加,符合程度逐渐改善.     

共面双对称条件下电子碰撞Ar原子单电离的一阶扭曲波Born近似

在共面双对称几何条件下,利用一阶扭曲波Born近似计算了中低能电子碰撞Ar原子(3p壳层电子)单电离的三重微分截面,并与最近的实验数据做了比较.结果表明,对于Ar原子,当入射电子能量比电离阈高40 eV以上,随着入射能量的增加,binary和recoil碰撞机理逐渐占据支配地位;在近阈能量范围,上述碰撞机理不再处于支配地位,扭曲效应明显.要完备地描述中低能入射条件下Ar原子的电子碰撞电离过程,理论模型必须同时考虑多种散射机理.     

Absolute cross-section measurements of inner-shell ionization

Cross section ratios for K- and L-shell ionization of thin silver and gold targets by positron and electron impact have been determined at projectile energies of 30–70 keV. The experimental results are confirmed by calculations in plane wave Born approximation (PWBA) which include an electron exchange term and account for the deceleration or acceleration of the incident projectile in the nuclear field of the target atom. We report first absolute cross sections for K- and L-shell ionization of silver and gold targets by lepton impact in the threshold region. We have measured the corresponding cross sections for electron (e^–) impact with an electron gun and the same experimental set-up.     

Inner-shell electron capture by impact of positron on the multi-electron atomic targets

The first-order Coulomb-Born approximation has been applied to the study of positronium formation through K-shell electron capture in the collision of positron with multi-electron atomic targets. The single-zeta Roothaan-Hartree-Fock wave functions are used to describe the electron initial bound states. The differential and total cross sections are computed for the impact of positron on helium, carbon, neon, sodium and argon atoms, with the formation of positronium in its ground state. For helium atoms, the calculated total cross sections are compared with the available experimental data and other theoretical calculations. The comparison shows a good agreement between the present calculations and the measurements.     

Semiclassical treatment of light-ion induced alignment of theL 3-subshell in heavy atoms

Light ion induced alignment measurements ofL ₃-subshell in heavy atoms are analyzed within the framework of the semiclassical theory of inner shell ionization. Coulomb deflection effects are exactly taken into account by hyperbolic classical orbits while the electron in the initial and final states is approximated by screened relativistic hydrogenic wave functions. Satisfactory agreement between experiments and theory is obtained for proton- and α-particle induced reactions within the whole region of bombarding energies.     

电子氢原子碰撞电离能量微分截面和总截面的理论计算

利用扭曲波玻恩交换（ＤＷＢＥ）近似方法对电子－氢原子碰撞电离截面进行了计算，计算所得总截面和能量微分截面均与最新的实验结果进行了比较，比较结果显示本计算与实验有较好的符合。还给出了能量微分截面的高斯拟合公式，文中对实验与理论计算存在的一些差距进行了讨论。 关键词：     

Mass Spectrometric Determination of Partial Ionization Cross Sections

A review of the measurement of partial electron impact ionization cross sections for rare gas atoms and molecules is presented, with particular regard to the low electron energy regime (<200 eV). Recently developed experimental techniques are surveyed. Predictions of quantal and classical approximations as well as some empirical formulae are compared with the experimental data. In conclusion a set of recommended atomic ionization cross sections is given for electron energies ranging from threshold up to 14 keV. Finally, the existence and measured appearance potentials for the production of doubly ionized rare gas dimers are discussed.     

Electronic relativistic effect on the ratios of deuteron to alpha-particle induced K-shell ionization cross sections

The ratios of the K-shell ionization cross sections induced by deuterons to those induced by α-particles with the same velocities have been calculated in the plane wave Born approximation using relativistic hydrogenic wave functions for the target electrons. The numerical results are compared with the recent experimental valus of Chang et al. The use of relativistic wave functios considerably improves the agreement with the experimental data.     

Empirical model for electron impact ionization cross sections of neutral atoms

A simple empirical formula is proposed for the rapid calculation of electron impact total ionization cross sections both for the open- and closed-shell neutral atoms considered in the range 1≤ Z≤92 and the incident electron energies from threshold to about 10⁴ eV. The results of the present analysis are compared with the available experimental and theoretical data. The proposed model provides a fast method for calculating fairly accurate electron impact total ionization cross sections of atoms. This model may be a prudent choice, for the practitioners in the field of applied sciences e.g. in plasma modeling, due to its simple inherent structure.     

Calculated cross sections for the single ionization of atoms (N, Cu, As, Se, Sn, Sb, Te, I, Pb) by electron impact

By correcting some primary parameters in the semi-classical Deutsch--M?rk (DM) formula, this paper calculates the absolute single electron-impact ionization cross sections of atoms N, Cu, As, Se, Sn, Sb, Te, I and Pb from threshold to 10000eV. The calculated cross sections are compared with available experimental data and other theoretical results. An excellent agreement was achieved between the calculated and measured cross sections for these atoms over a wide range of impact energies.     

Inner-shell ionization by positron and electron impact

Measurements of relative cross sections of K- and L-shell ionization of silver and gold targets by positron and electron impact at projectile energies of 30–70 keV are reported. The experiments were performed at the slow positron source TEPOS at the linac of the Strahlenzentrum. This source and the experimental equipment will be described briefly and the experimental results will be presented in detail. In addition, plane wave Born (PWBA) calculations were performed. They include an electron exchange term and the deceleration or acceleration of the incident projectile in the nuclear field of the target atom. The present experimental results agree well with these calculations; for L-shell ionization, they are at variance with a previous experiment where a different energy dependence was observed.     

Electron ionization cross sections for neutral fullerene C70

The energy dependent ionization cross sections corresponding to the formation of singly, doubly and triply charged cations in the electron impact ionization of C₇₀ are evaluated employing a semiempirical formulation at the incident electron energies of 100 and 200 eV. The integral ionization cross sections have also been calculated in the energy range varying from ionization thresholds to 1000 eV which revealed a satisfactory agreement with the available experimental and the theoretical data. The ionization rate coefficients corresponding to the various cations have also been evaluated using the presently calculated ionization cross sections and Maxwell-Boltzmann energy distributions.     

低能质子引起的金LX射线相对产生截面

对于能量为０．５－１ＭｅＶ的入射质子，在计算中采用ＡｕＬ１次壳层荧光产额的实验值代替相应的Ｄｉｒａｃ－Ｈａｒｔｒｅｅ－Ｓｌａｔｅｒ值时，使用ＲＰＷＢＡ－ＢＣ（经结合能和库仑歪曲修正的相对论平面波玻恩近似）电离截面计算得到的金原子ＬＸ射线相对产生截面与测量值相符。以前报道的对ＲＰＷＢＡ－ＢＣ截面的各种修正都是不需要的     

Single and double ionization of neon 2s- and 2p-subshells by proton and electron impact

Absolute single and double ionization cross sections of neon 2s- and 2p-subshells for proton (40–900 keV) and electron impact (0.2–10 keV) have been measured using photon spectroscopy in the spectral range of the vacuum ultraviolet. Cross sections for double ionization decrease more rapidly with increasing impact energy than cross sections for single ionization. No definite asymptotic energy dependence of a Bethe-Fano-plot could be found for double ionization in contrast to single ionization. The experimental results are compared with theoretical predictions of the shake-off model and Gryzinski's classical binary encounter theory. Better agreement is found with the latter, indicating that successive binary collisions have to be considered as a strong mechanism for double ionization by protons or electrons of the investigated energy range. Comparison is made with other experimental results for double ionization by photon impact or capture ionization by proton impact.     

Single differential and total ionization cross section of the helium atom by positron impact

Single differential (SDCS) and total (TCS) cross sections are calculated for the single ionization process of a helium atom by positron impact in the intermediate and high energy range (50–300 eV). To study the charge asymmetry, cross sections for electron impact ionization are also presented for comparison with the positron data. The TCS results for positron impact have been compared with existing measurements. A good agreement is noted in the high energy regime ( 100–300 eV).     

N‐shell ionization cross sections by proton impact in the BEA

The N‐subshell ionizations cross sections of heavy elements by proton impact have been calculated in the binary‐encounter approximation. The momentum distribution of target electrons is taken into account by the use of the nonrelativistic and relativistic hydrogenic models and the Hartree–Fock–Roothaan and the relativistic Hartree–Fock–Roothaan methods. The obtained subshell ionization cross sections are compared with the experimental data and other theoretical calculations. The electronic relativistic effect and the wave‐function effect on N‐shell ionization cross sections are discussed.     

K-shell single-electron capture in collision of fast protons with multi-electron atoms

Single-electron capture from the K shell of atomic targets by impact of protons at moderate and high energies has been studied using a first-order three-body Coulomb-Born continuum distorted wave approximation. The applied formalism satisfies the correct Coulomb boundary conditions. Single-zeta Roothaan-Hartree-Fock wave functions are used to describe the initial electronic bound state of the exchanged electron. Both differential and integral capture cross sections are calculated for impact of protons on carbon, nitrogen, oxygen, neon and argon atoms. The results are compared with the available measurements and other theories. The agreement between the calculations and experimental data is remarkable.     

Calculations of total ionization cross sections of Ne,Ar, Kr,and Xe atoms in the born approximation allowing for electron perturbations in the continuous spectrum

Electron impact ionization cross sections of Ne, Ar, Kr, and Xe atoms are numerically calculated. The electron perturbation in the continuous spectrum in the target field is taken into account. The matrix elements are calculated in many-electron, nonrelativistic approximation with allowance for the superposition of configurations and relaxation effect. The radial part of the electron wave function in the continuum is calculated by solving the single-configuration Hartree-Fock equation. The wave functions of electrons in the continuum are orthogonalized with respect to the core orbital functions. The calculated cross sections are compared to the experimental data and calculations made using the plane-wave Born approximation and that involving generalized oscillator strengths.     

Photoionization of CF4 in the VUV region

We present calculated results of photoionization cross sections and photoelectron angular distributions for ionization out of the five outermost valence orbitals of CF₄ for photon energies ranging from near threshold to 55 eV. The Schwinger variational iterative method, using an exact static-exchange plus a model correlation–polarization potential, is applied to obtain the continuum photoelectron orbitals. The quantitative agreement between our calculated results and the experimental data is fair. Moreover, our study is capable of identifying most structures seen in experimental results for both cross sections and asymmetry parameters.